Suryappa Jayappa Pawar

In this study, the impacts of the inclusion of two semi-circular baffles and their orientations on the acoustic performance of the side outlet muffler have been investigated. The side outlet muffler has a circular simple expansion chamber with an axial inlet and a side outlet and two semi-circular baffles that have been placed inside the expansion chamber at different orientations. The axis of the outlet is at the right angle to the axis of the inlet. The acoustical investigation of the side outlet muffler with two semi-circular baffles is done using the plane wave analysis, the finite element method (FEM), and the two-load technique. Based on the orientations of the two semi-circular baffles, three different models of side outlet muffler with semi-circular baffles have been investigated. The plane wave analysis, FEM, and two-load method are applied to all models and it is found that analytical, computational, and experimental transmission loss (TL) are in good agreement. The analytical modelling successfully predicts the presence of semi-circular baffles in the form of peaks and troughs in the TL of side outlet muffler with semi-circular baffles before the cut-off frequency and thus proves its effectiveness. Among all the models, model 2 gives 42% higher TL than model 1 and model 3 shows 16.20% higher TL than model 2. Hence, model 3 proves to be the best design for the side outlet muffler with semi-circular baffles in the attenuation of noise. The model 3 is effective for 1030 Hz–1480 Hz, 1500 Hz–1570 Hz, and 1640 Hz–2400 Hz frequency sound waves. The TL curve, sound pressure contours for model 3, and the band power variation in the 1/3 octave band for all the models have also been presented.

The acoustic behaviour of a classroom is vital for an effective teaching-learning process. The present work aims to experimentally determine the acoustic performance of a typical classroom. The full-scale experiment was conducted at the Seminar Hall, the Department of Applied Mechanics, MNNIT Allahabad, Prayagraj, using a method with limited resource requirements. The Seminar Hall was divided into four planes by threads, and the sound pressure level (SPL) was measured at 30 coordinates in each plane for the specified sound source location. Data were collected from three different sound source locations. The study revealed that the sound source location and frequency significantly influence the sound pressure levels in the classroom, impacting its acoustic performance. The broader implications of interior materials, such as wall material and the position of elements like the teaching board, door, and podium, are highlighted as critical considerations for future classroom acoustic optimization. Furthermore, a numerical model was developed to predict the variation in the SPL with change in the sound source locations and frequencies. The collected data validated with the finite element (FE) model. The verification experiments for the modeling results were performed for each plane. The results of the FE model and experiments were found consistent across all four planes of the seminar hall and the various sound source locations.

The present study reports a cost‐effective and eco‐friendly route for the one‐pot biogenic synthesis of zinc oxide (ZnO) nanoparticles (ZnO NPs) using Ficus racemose leaf extract. The average particle size distribution and zeta potential were reported as 200 nm and −10.47 mV via dynamic light scattering (DLS) and zeta potential. The single‐phase patterns of ZnO NPs showing hexagonal crystal structure with an average crystallite size of 21 nm were measured via X‐ray diffraction (XRD). Field emission scanning electron microscopy (FESEM) revealed the cubical and cuboidal morphology of NPs with an average size of 95–220. In contrast, transmission electron microscopy (TEM) and selective area electron diffraction (SAED) revealed the d‐spacing value as 0.247 to confirm the formation of ZnO NPs. The maximum wavelength for ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy were observed at 355 nm and 556 nm, respectively. Functional groups containing flavonoids and polyphenols as reducing agents for the reduction and synthesis of ZnO NPs were verified through Fourier transform infrared (FTIR) spectroscopy. ZnO NPs were also evaluated for their strong antibacterial property against Staphylococcus aureus (12 ± 0.69 mm) and Escherichia coli (11 ± 0.83 mm). This can be employed in numerous biological and biomedical domains, such as preventing bacterial growth.

Elium (novel methyl methacrylate (MMA)) resin is a liquid thermoplastic resin curable at room temperature and a possible replacement for epoxies. The main objective of this work is to evaluate the mechanical characteristics of novel Kevlar fabric reinforced Elium composites with different thicknesses. The plain-woven structure Kevlar/Elium laminates were manufactured with 1.5 mm and 2.5 mm thicknesses through vacuum-assisted resin infusion moulding, where 8 and 12 layers of woven fabrics were used, respectively. The effect of laminate thickness was measured in terms of mechanical (tensile, flexural, shear, and dynamic mechanical analysis (DMA)) and physical (density and fibre volume fraction (FVF)) characteristics. The density of the laminates was found in the range of 1.18–1.31 g cm⁻³. FVF was 50.69 and 52.27% for 1.5 and 2.5 mm thick laminates, respectively. The composite with 1.5 mm thickness exhibited the highest tensile strength (667.9 MPa) and flexural strength of 330.7 MPa. Conversely, the highest interlaminar shear strength measured for 2.5 mm thick laminate is 16.5 MPa. The DMA analysis recorded the highest storage and loss modulus for 2.5 mm thickness laminates. The fractography analysis confirmed the quantified experimental observation of excessive interface debonding and delamination. Elium composites may be suitable for high-end structural applications, including marine and aircraft structures.

In this study, an investigation on the acoustic performance of a simple expansion chamber muffler with side outlet has been presented. The investigation for the muffler is done in the 10–2400 Hz frequency range. The muffler is analyzed analytically, computationally, and experimentally. The computational and analytical modellings of the muffler have been done by using the finite element and transfer matrix methods, respectively for the determination of transmission loss. As the transfer matrix method is unable to capture the higher order modes above the cut-off frequency of the muffler, the finite element method has been adopted as the computational method. Additionally, the accuracy in the analytical and computational modelling of the muffler is checked with the experimental investigation. The two-load method is used in this study for muffler to determine the transmission loss and band power. The side outlet of the muffler introduces an extra impedance due to the shunt element and hence the effectiveness of the muffler can be improved. This muffler shows an overall improvement of 24.73 dB in the transmission loss when compared with the transmission loss of the simple expansion chamber muffler with an axial outlet in 10–2400 Hz frequency range. Specifically, the simple expansion chamber muffler with side outlet is more effective than the simple expansion chamber muffler with an axial outlet in 350–680 Hz, 1040–1350 Hz, 1570–1590 Hz, and 1850–2400 Hz frequency ranges. The comparison among the different techniques shows a fair agreement in the results. The transmission loss, variation of the band power in the 1/3rd octave band, and sound pressure level contours for the muffler at the selected frequencies have been presented. This study offers an advantage in the design of the automotive mufflers.

Sound absorbers play a significant role in keeping a quiet and noise-free environment. Both synthetic and natural materials can use to control noise. Currently, natural materials are a valid alternative to conventional synthetic materials. This paper aims to study the physical parameters of Grewia Optiva fibers. The theoretical models’ assessment has been carried out to calculate the sound absorption coefficient with the help of Scilab software for synthetic (melamine foam, polyurethane foam, and mineral wool) and natural (kenaf fiber, coir fiber, and Grewia Optiva fiber) materials. The results from the simulation conclude that the sound absorption coefficient of Grewia Optiva fiber is almost similar to or much better than other synthetic and natural sound absorbers. Hence, Grewia Optiva fibers can be a valid substitute for traditional sound absorbers for sound absorption purposes.